The invention relates to a sports boot in the form of a rigid upper composed of a collar articulated on a shell surrounding the foot, which is provided with a device for locking or blocking the collar on the shell in order to lock or block the collar relative to the shell in a first position for practicing the sport and for unlocking the collar relative to the shell and allowing the amplitude of movement thereof relative to the shell to be increased in a second position when the sport is not being practiced, for example in order to make it easier to put the boot on the foot and to walk. The invention also relates to a device for locking and unlocking a collar on a shell as such for a sports boot.